"Say out-loud the color of the word" is the typical instruction in the Stroop Task. The trick is that when when green is in green font, people have no problem with answering correctly under time pressure. However, when green is in red font, people stumble because we read faster than we think about the color. Illiterate people have no problem with correctly naming the color of the word, as they can't read.
The Stroop Task is used in psychology experimental studies and, in the huge majority of cases, is irrelevant in the real world.
However, I came across a case in which the Stroop effect influences real-life interactions of customers (passengers) with a service.
In the Washington DC Metro Area public transportation (WMATA), subway lines are color coded (e.g. the Blue line, the Orange line). However, the displays on both the outside and the inside of the metro-trains violate the principle of cognitive fluency. The outside displays are in either white or yellow, while the inside displays are in red. Moreover, all train-car bodies are silver on the outside.
Services need to be intuitive as much as possible. For this, service designers need to understand human intuition.